Statistically distributed nano-scratch testing of AlFeMnNb, AlFeMnNi, and TiN/Si₃N₄ thin films on silicon

For studying the damage tolerance of thin films, a novel randomly distributed nano-scratch test method was introduced and demonstrated as a promising characterization method. It is capable of more closely simulating the damage progression in abrasion, where material removal can be influenced by the interaction between damage produced by previous scratches in close proximity. In addition to studying how localized failure events affect subsequent damage progression, it is possible to monitor the evolution of the film degradation cycle-by-cycle using the mean depth and friction over the scratch. Randomly distributed nano-scratch tests were performed on the high entropy alloy AlFeMnNb, AlFeMnNi, and nanocomposite (nc-) TiN/Si3N4 thin films on silicon. Brittle fracture and film removal with extensive chipping of the Si substrate were observed over the entire scratched region on AlFeMnNi and nc-TiN/Si3N4 in distributed scratch tests at applied loads that were only similar to 0.2-0.3 of the load needed to produce the chipping in ramped load nano-scratch tests due to film and substrate fatigue. In contrast, the softer AlFeMnNb deformed predominantly by ductile ploughing with significantly improved damage tolerance and crack resistance in the distributed scratch tests. The new method can be used to evaluate the performance of thin films in applications where they can be exposed to abrasive/sliding wear. It can provide a more direct measure of abrasion resistance than assuming high resistance to abrasive wear from coating hardness. In the thin film systems studied, higher hardness was associated with greater fracture and delamination in the distributed scratch tests.